This invention relates to valves and more particularly, to gate valves for controlling the flow of high temperature fluids.
There are many applications in which it is necessary to precisely control the flow of high temperature fluids. In one particular application, it is necessary to selectively block fluid flow of high temperature methane gas between the reactor and incinerator in the production of thermal black. Metal valving elements have been used in the past in these types of applications. However, they are subject to corrosion, errosion, and warpage which reduces the ability of a valve to properly control the gases. Water cooling systems have been used in an attempt to minimize these undesirable characteristics but in general they have been troublesome and greatly increase the operating cost of the valve.
In one attempt to solve this problem, the prior art attempted to utilize silicon carbide refractory material for the valve element. In U.S. Pat. No. 3,837,356 there is disclosed a "goggle" type valve in which a pivotally movable gate member is sandwiched between two stationary goggle-type sections. Goggle valves such as the one disclosed in this patent have several disadvantages. For example, the gate member must be at least twice as large as the fluid flow opening in the valve. Because of the relatively complex housing and actuating mechanism in this goggle valve, the gate member was, for all practical purposes, restricted to a relatively small size, typically, about 6 to 12 inches in diameter.
Despite all of its disadvantages, those skilled in the art believe that the goggle-type valve was the only practical construction for utilizing relatively fragile refractory material for the gate member since the goggle valve provided support for the sliding gate member over a substantial area. This patent teaches that silicon carbide provides a gate member which is relatively durable, errosion resistant and capable of withstanding thermal shock. It has been discovered that silicon carbide when used in very demanding applications, such as the one noted above, still does not possess the necessary characteristics. In actual use, it has been discovered that silicon carbide can deteriorate within a relatively short period of time and permit an unacceptable amount of leakage when the valve is supposedly closed. Moreover, it is difficult, if not impossible, to readily construct gate valves much in excess of 24 inches from silicon carbide without experiencing an untolerable level of cracks and other properties which would render it unacceptable in use.